In electronic devices, critical data, such as time stamps, counters or other state values, is often stored in the general system non-volatile memory (NVM). FLASH memory is an example of non-volatile memory. This makes the data vulnerable to tampering. Encrypting the data before storage does not solve the problem because an encrypted value could be copied and used to overwrite a new encrypted value at some later date, thereby resetting the data value to a previous state.
Physical tamper protection, such as storing values in non-volatile memory that is on the application processor provides a solution, but is difficult to implement and expensive. Thus, this approach is impractical for commercial electronic devices. This approach has been used in so-called Smartcards, in which critical data is stored in non-volatile memory located on the same substrate as the main processor. However, application processors on mobile devices do not have on-board non-volatile memory, so the state data values must be stored in external non-volatile memory.